This study is designed to evaluate the vector competence of Culiseta melanura for WEE virus and to examine the role of this mosquito in certain aspects of the ecology of this virus in the Northeast. The susceptibility and transmission ability of C. melanura for WEE virus will be quantitated in the laboratory using a colonized strain of this mosquito. The susceptibility of other selected mosquito species that occur in the Northeast is also being studied to develop a comparative basis for evaluating vector ability. The role of C. melanura in the winter survival of WEE virus in the Northeast will be examined by evaluating the ability of experimentally infected C. melanura to passage virus to eggs and F1 progeny. The influence of feeding behavior of this mosquito and the kinetics of virus replication in this mosquito at various temperatures will be studied in relation to the characteristic seasonal pattern of enzootic virus activity that occurs in the Northeast. Biological markers that distinguish strains of WEE virus from the eastern and western U.S. will be studied and the stability of such markers after serial passage of virus strains through C. melanura and Culex tarsalis will be evaluated.